Compound semiconductor materials of group III and group V elements (referred to as III-V compound semiconductors hereinafter) are good candidates for forming transistors due to their high electron mobility. III-V compound semiconductor films, however, are typically grown on other substrates because it is difficult to obtain bulk III-V compound semiconductor crystals. The growth of III-V compound semiconductor films on dissimilar substrates faces difficulties because these substrates can have lattice constants and thermal expansion coefficients different from that of the III-V compound semiconductors.